In stalk-like harvested crop machines, such as balers and self-loading forage boxes, there is, in many cases, a need for cutting the harvested crop into shorter pieces before storing it. For this purpose, cutter heads are used that have a number of knives arranged side-by-side alongside each other extending into a channel in which the harvested crop is conveyed. In order to change the length of cut the number of knives, in each case, are moved into the channel or out of it.
DE 38 16 204 A describes a round baler with a cutter head, in which the knives, arranged in a row, are connected, so as to pivot, around their upstream ends about a horizontal axis, in which the harvested crop is to be conveyed into the baling chambers. The knives include a recess into which a first roll engages with knives in the active position, that is connected in joints to a first arm of a lever associated with the knife, that is supported, so as to rotate, about an axis parallel to the pivot axis. A spring pre-loads each of the first arms of the lever with the roll in the direction of the knife. The lever includes a second arm with a further roll. A control shaft extending parallel to the axis is equipped with several curved disks that interact with the further rolls and are able to bring the levers into a non-operating position, in which the first roll is spaced at a distance from the recess at the back of the knife and the knife is pivoted out of the conveying channel that is, it is in the inactive position. If the curved disk does not bring the lever into the non-operating position, then the spring draws the associated knife into the operating position, in which it extends into the conveying channel and cuts the harvested crop. In case of an overload, for example, due to a foreign object taken up, the first roll is forced out of the recess against the force of the spring and the knife reaches the inactive position.
Accordingly, the control shaft is used to bring the levers of the knives that are to be brought into the inactive position against the force of the spring associated with the levers. Due to the high forces a reduction gearbox is required in order to be able to rotate the control shaft manually. Alternatively, an actuator, actuated by external forces is used for this purpose in the form of a hydraulic cylinder. A disadvantage here in particular is seen in the fact that the forces acting on the curved disk will require a very stable and therefore costly dimensioning of the curved disk of the control shaft in order to avoid premature wear.